Thin film resonator and method for manufacturing the same

ABSTRACT

A thin film resonator having enhanced performance and a manufacturing method thereof are disclosed. The thin film resonator includes a supporting means, a first electrode, a dielectric layer and a second electrode. The supporting means has several posts and a supporting layer formed on the posts. The first electrode, the dielectric layer and the second electrode are successively formed on the supporting layer. The thin film resonator is exceptionally small and can be highly integrated, and the thickness of the dielectric layer of the resonator can be adjusted to achieve the integration of multiple bands including radio, intermediate and low frequencies. Also, the thin film resonator can minimize interference and has ideal dimensions because of its compact substrate, making the thin film resonator exceptionally small, yet comprising a three-dimensional, floating construction.

TECHNICAL FIELD

[0001] The present invention relates to a thin film resonator and amethod for manufacturing the same, and more particularly to anintegrated thin film resonator with multiple bands to enhanceperformance and an easy method for manufacturing the same.

BACKGROUND ART

[0002] Mobile communications has been rapidly developed as the maininstrument serving the information society. This instrument has beeninfluenced by the developments of two technologies: signal processingusing modulation or demodulation of transmitted data over limitedfrequency bands, and the technology of manufacturing radio frequency(RF) hardware parts.

[0003] In particular, filters are most important among the parts usedfor RF mobile communication devices. Filters are able to select thesignal requested by the user from numerous signals on the publiccommunication network, or filter a signal transferred by the user. Thus,excellent filters were previously developed for high quality mobilecommunication. Recently, higher performance filters have been developedto be thinner and more light-weight. These features ensure that mobilecommunication devices consume less power and more portable.

[0004] In general, a resonator or a frequency filter is the device thattransmits the frequencies of a message in a predetermined band, andfilters the frequencies on other bands being produced by variouselectronic devices such as wireless phones, personal communicationservice devices, cellular phones or devices for the international mobiletelecommunications 2000 (IMT-2000) as a band pass filter.

[0005] Presently, the dielectric filter and the surface acoustic wave(SAW) filter are widely used as the RF filter for mobile communicationdevices. The dielectric filter has some advantages such as highpermeability, low insertion loss, stability at high temperatures andgood mechanical strength. However, the dielectric filter is too large tobe applied in a monolithic microwave integrated circuit (MMIC). Thoughthe mono-blocked or the multi-layered surface mounted device (SMD)resonators are now developed with smaller dimensions, SMD resonators donot sufficiently overcome their size problems.

[0006] SAW filters are relatively smaller than dielectric filters andhave simpler signal processing and more simplified circuits. The SAWfilter also can be manufactured using semiconductor technology, andgives high quality results since the SAW filter's side rejection in itspass-band is greater than that of the dielectric filter. However, theSAW filter has large insertion losses below 3 dB and its manufacturingcosts are high because it is manufactured using single crystal I5piezoelectric substrate composed of lithium niobate (LiNbO₃) or lithiumtitanate (LiTaO₃). Also, the SAW filter is manufactured using anultraviolet ray exposure apparatus so that the SAW filter may not beused for high frequency bands above 5 GHz because the line width of theinter-digital transducer (IDT) is above 0.5 μm.

[0007] Film bulk acoustic resonators (FBAR) have been developed for nextgeneration mobile communication devices. The FBAR can be mass-producedat low cost using semiconductor technology and is ultra light weight andthin. In addition, the FBAR can be freely combined with RF activedevices. In particular, the FBAR has good insertion loss of about 1 to1.5 dB-smaller than or identical to that of the dielectric filter. TheFBAR also has excellent side rejection higher than the of the SAW filterby about 10 to 20 dB, thereby providing high quality results.

[0008] At present, the active elements of mobile communications includethe Hetero-junction Bipolar Transistor (HBT) or the Metal SemiconductorFiled Effect Transistor (MESFET), but these are gradually beingsimplified and minimized by monolithic microwave integrated circuit(MMIC) technology. However, passive components of RF technology such asthe filter, the duplexer filter or the antenna are relatively large andcomplicated structures so that the single chip may not be achieved dueto passive components.

[0009] The FBAR or the stacked thin film bulk wave acoustic resonators(SBAR) are manufactured by forming piezoelectric material such as zincoxide (ZnO) or aluminum nitride (AIN) on a substrate composed of siliconor gallium-arsenic (Ga—As) using RF sputtering method, thereby achievingthe desired resonance provided by the piezoelectric material.

[0010] The thin film resonator can be manufactured at low cost and yetprovide high quality, making it is applicable for use in various deviceswith frequency bands of 900 MHz to 10 GHz. In addition, the thin filmresonator can be much smaller than the dielectric filter and has theadded benefit of an insertion loss smaller than that of the SAW filter.Hence, a thin film filter such as FBAR can be used in any MMIC dependenton high quality and good stability.

[0011] The method for manufacturing conventional FBAR or the SBAR isdisclosed at U.S. Pat. No. 6,060,818 issued to Richard C. Ruby et al.

[0012]FIG. 1 is a cross-sectional view showing the FBAR and FIGS. 2A to2C are cross-sectional views illustrating the method for manufacturingthe FBAR in FIG. 1.

[0013] Referring to FIG. 1, the FBAR 10 is formed on a silicon substrate15 and the FBAR 10 includes a bottom electrode 20, a piezoelectric layer25 and a top electrode 30.

[0014] An oxide layer 35 is formed on the substrate 15 and a pit 40 isinterposed between the substrate 15 and the FBAR 10.

[0015] Referring to FIG. 2A, the silicon substrate 15 is provided, andthen the pit 40 having a predetermined depth is formed on the substrate15 by partially etching the substrate 15. Subsequently, the oxide layer35 is formed on the whole surface of the substrate 15 by the thermaloxidation method.

[0016] As shown in FIG. 2B, after a sacrificial layer 45 composed ofphosphor silicate glass is coated on the oxide layer 35 to fill the pit40, the sacrificial layer 45 is polished so that the sacrificial layer40 remains only in the pit 40.

[0017] Referring to, FIG. 2C, after the bottom electrode 20 composed ofmolybdenum (Mo), the piezoelectric layer 25 composed of aluminum nitride(AIN), and the top electrode 30 composed of molybdenum are successivelycoated on the oxide layer 35 and on the sacrificial layer 45 filling thepit 40, the bottom electrode 20, the piezoelectric layer 25, and the topelectrode 30 are patterned. Then, the sacrificial layer 45 is removedusing an etching solution containing hydrofluoric acid (HF), therebycompleting the FBAR 10 as shown in FIG. 1.

[0018] The conventional FBAR is, however, formed on the substrate wherethe cavity is positioned, giving the FBAR two-dimensional construction.Hence, the conventional FBAR provides poor quality performance with anincreased insertion loss.

[0019] In addition, the interference of the substrate may not beblocked, causing the power loss of the FBAR to increase. The size of theFBAR is limited also, since the FBAR is formed over the cavity in thesubstrate in order to receive the deformation of the piezoelectriclayer.

[0020] Furthermore, the process for etching the silicon substratedemands much time, and the cost of manufacturing the FBAR increasesbecause the conventional FBAR is formed on the silicon substrate wherethe cavity is positioned.

[0021] To overcome such problems, research institutes at Berkeley andMichigan Universities have disclosed a thin film bulk acoustic resonator(TFBAR) with a three-dimensional structure on a substrate using themicro-electromechanical system (MEMS) technology. However, the TFBAR maynot be mass-produced and packaging the TFBAR may be difficult since itsstructure is complicated and the integration device including the TFBARis difficult.

[0022] Disclosure of the Invention

[0023] The present invention is intended to overcome the disadvantagesdescribed above. Therefore, it is an object of the present invention toprovide a thin film resonator having an ultra minute size in order toachieve high integration with MEMS technology, and a method formanufacturing the thin film resonator.

[0024] It is another object of the present invention to provide a thinfilm resonator manufactured to be a multiple frequency band integratedthin film resonator by controlling the thickness of piezoelectric layerthereof, and a method for manufacturing the thin film resonator.

[0025] It is still another object of the present invention to provide athin film resonator having a three-dimensional, floating construction tominimize power loss due to interference from the substrate,corresponding in size to the size of the substrate, and a method formanufacturing the thin film resonator.

[0026] It is still another object of the present invention to provide athin film resonator manufactured at low cost, yet giving high qualityresults, and a method for manufacturing the thin film resonator.

[0027] It is still another object of the present invention to provide athin film resonator having minute patterns and a three-dimensional formin order to obtain high quality results with low insertion loss, and amethod for manufacturing the thin film resonator.

[0028] To accomplish the objects of the present invention according toone aspect of the present invention, there is provided a thin filmresonator for filtering the frequency of a predetermined band comprisinga supporting means having a plurality of posts formed on a substrate anda supporting layer formed on the posts, a first electrode formed on thesupporting means, a dielectric layer formed on the first electrode, anda second electrode formed on the dielectric layer.

[0029] There are four posts formed on the substrate so as to support thesupporting layer, and the supporting layer has a plurality of openingsformed adjacent to each post, respectively.

[0030] Preferably, the supporting layer, the first electrode, thedielectric layer and the second electrode are each shaped likerectangular plates that, in combination, create a pyramid shape.

[0031] The first and the second electrodes are composed of metalsselected from the group consisting of platinum, tantalum,platinum-tantalum, gold, molybdenum and tungsten. The dielectric layeris composed of materials selected from the group consisting of bariumtitanate, zinc oxide, aluminum nitride, lead zirconate titanate (PZT),lead lanthanum zirconate titanate (PLZT) and lead magnesium niobate(PMN).

[0032] The thin film resonator further comprises a connecting means forconnecting the second electrode to a circuit formed on the substrate.The connecting means has a central portion and lateral potions bent fromthe central portion so that the connecting means contacts the circuitand the second electrode. As a result, a first air gap is interposedbetween the substrate and the supporting means and a second air gap isinterposed between the second electrode and the connecting means. Inthis case, the connecting means is composed of metals selected from thegroup consisting of platinum, tantalum, platinum-tantalum, gold,molybdenum and tungsten.

[0033] To accomplish the objects of the present invention according toanother aspect of the present invention, there is provided a method formanufacturing a thin film resonator for filtering frequencies on apredetermined band, which comprises the steps of forming a firstsacrificial layer on a substrate, partially etching the firstsacrificial layer to expose portions of the substrate, forming aplurality of posts on the exposed portions of the substrate, forming afirst layer on the posts and the first sacrificial layer, forming afirst metal layer on the first layer, forming a second layer on thefirst metal layer, forming a second metal layer on the second layer,forming a first electrode, a dielectric layer and a second electrode bypatterning the second metal layer, the second layer and the first metallayer, forming a supporting layer having a plurality of openings bypatterning the first layer, and removing the first sacrificial layerthrough the openings.

[0034] The first sacrificial layer is composed of poly silicon andformed by a low pressure chemical vapor deposition method and the firstsacrificial layer is partially etched by a photolithography method, areactive ion etching method or an argon laser etching method.

[0035] The posts are created through forming a BPSG layer on the firstsacrificial layer and the substrate using a low pressure chemical vapordeposition method at temperatures under about 500° C., and polishing theBPSG layer to remove portions of the BPSG layer formed on the firstsacrificial layer. At that time, the BPSG layer is polished by achemical mechanical polishing method or an etch-back method.

[0036] The first layer is formed by a plasma enhanced chemical vapordeposition method or by using silicon oxide or phosphor oxide attemperatures from approximately 350 to 450° C.

[0037] The first and the second electrodes are formed by using metalsselected from the group consisting of platinum, tantalum,platinum-tantalum, gold, molybdenum and tungsten using a sputteringmethod or a chemical vapor deposition method.

[0038] The second layer is formed from piezoelectric material orelectrostrictive material using a sol-gel method, a sputtering method, aspin coating method or a chemical vapor deposition method. The secondlayer is composed of materials selected from the group consisting ofbarium titanate, zinc oxide, aluminum nitride, lead zirconate titanate(PZT), lead lanthanum zirconate titanate (PLZT) and lead magnesiumniobate (PMN). In this case, the second layer is heat treated by a rapidthermal annealing method for the phase transition of the second layer.

[0039] The first sacrificial layer is removed with xenon fluoride orbromine fluoride.

[0040] Preferably, the method for manufacturing the thin film resonatorcomprises the steps of forming a second sacrificial layer on thesubstrate and the second electrode, partially etching the secondsacrificial layer to expose a portion of the second electrode and acircuit formed on the substrate, forming a connecting means forconnecting the second electrode to the circuit, and removing the secondsacrificial layer.

[0041] The second sacrificial layer is composed of poly silicon or photoresist and formed by a low pressure chemical vapor deposition method ora spin coating method.

[0042] Preferably, the surface of the second sacrificial layer isplanarized using a chemical mechanical polishing method or an etch-backmethod.

[0043] The connecting means is formed from metals selected from thegroup consisting of platinum, tantalum, platinum-tantalum, gold,molybdenum and tungsten using a sputtering method or a chemical vapordeposition method.

[0044] The second sacrificial layer is removed with xenon fluoride,bromine fluoride, etching solution containing hydrofluoric acid, or byusing an argon laser etching method. At that time, the steps forremoving the first and the second sacrificial layers are simultaneouslyperformed.

[0045] In general, the resonator for filtering frequencies on a bandoperates according to the principle of resonance created due to a bulkacoustic wave generated from the piezoelectric layer that lies betweentwo electrodes. The process for manufacturing such a resonator generallyconsists of forming the piezoelectric film composed of zinc oxide (ZnO)or aluminum nitride (AIN) on a substrate composed of silicon orgallium-arsenic (Ga—As), and forming a membrane and electrodes.

[0046] In the resonator manufacturing process, the piezoelectric film isfixed to the electrode and the piezoelectric film is adequately thin andflat, and of adequately high density. According to the conventionalmethod, after the P⁺ layer including a boron or silicon oxide layer, isformed on the silicon substrate by an ionic growth method, the bottom ofthe silicon substrate is anisotropically etched until the membrane formsa cavity formed in the substrate. Then, electrodes are formed on themembrane and the piezoelectric layer is interposed between theelectrodes by using an RF magnetron sputtering method to form the thinfilm resonator. The piezoelectric materials used to form thepiezoelectric layer requires a high specific resistance below 106 Ωcmwith a standard deviation below 60, a large electromechanical couplingconstant, and good cultivation. In addition, the piezoelectric materialshould have high breaking strength and quality reproduction results.However, the manufacturing process, including production of theabovementioned membrane products, experiences much failure because themembrane may be fractured when the thin film resonator is separated forpackaging. Also, the thin film resonator may have low resonancecharacteristics because acoustic wave energy is lost due to themembrane. Recently, an air gap typed FBAR or a brag reflector typed FBARhas been used to reduce this loss of acoustic wave energy due to themembrane, and to simplify the resonator manufacturing process.

[0047] As for the air gap type of FBAR, after a sacrificial layer isformed on a silicon substrate using micro-machining technology, the airgap is formed at the point where the sacrificial layer is located.Hence, the manufacturing time and the generation of harmful gases can bereduced without using back-etching to form the membrane.

[0048] In the brag reflector typed FBAR, materials, each with differentacoustic impedances, are alternatively formed on the silicon substrateto facilitate the brag reaction, thereby generating the resonance of theacoustic wave energies between electrodes. The brag reflector typed FBARcan be utilized as a ladder filter, a monolithic crystal filter, astacked filter or a lattice filter can be a one chip type of thin filmresonator. Such resonators may be manufactured quickly and have highmechanical strength, but their low electromechanical coupling constantis reduced by 30% when compared to the conventional FBAR.

[0049] According to the present invention, the thin film resonator ismanufactured using MEMS technology without etching the substrate to haveminute dimensions below hundreds of micrometers. Hence, the thin filmresonator is exceptionally small and can be highly integrated onto thesubstrate. Also, the thickness of the dielectric layer of the thin filmresonator can be adjusted to achieve the integration of multiple bandsincluding radio frequency (RF), intermediate frequency (IF) and lowfrequency (LF) by controlling the thickness of the dielectric layer.Also, an inductor and a capacitor can be integrated.

[0050] In addition, yields can be increased and manufacturing costs canbe greatly reduced since the thin film resonator can be manufacturedwithout etching or machining the silicon substrate. Therefore, themanufacturing process of the present invention has excellent advantagesduring mass production, including simplicity and ease of packaging.Also, the thin film resonator of the present invention has a goodquality factor of about 1000 to 10000 and a low insertion loss of under2 dB, because the thin film resonator has minute patterns and athree-dimensional, floating construction, and is easily manufacturedusing the MEMS technology.

[0051] Furthermore, the thin film resonator of the present invention canminimize any interference due to its substrate, and has ideal dimensionsbecause of its compact substrate, making the thin film resonatorexceptionally small yet comprising three-dimensional, floatingconstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The above objects and other advantages of the present inventionwill become more apparent through the detailed description of thepreferred embodiments thereof with reference to the attached drawings inwhich:

[0053]FIG. 1 is a cross-sectional view showing the conventional filmbulk acoustic resonator;

[0054]FIGS. 2A to 2C are cross-sectional views illustrating a method formanufacturing the conventional film bulk acoustic resonator in FIG. 1;

[0055]FIG. 3 is a perspective view showing a thin film resonatoraccording to one preferred embodiment of the present invention;

[0056]FIG. 4 is a cross-sectional view showing the thin film resonatorin FIG. 3; and

[0057]FIGS. 5A to 5I are cross-sectional views illustrating a method formanufacturing the thin film resonator in FIG. 4.

BEST MODES FOR CARRYING OUT THE INVENTION

[0058] Hereinafter, preferred embodiments of the present invention willbe described in more detail with reference to the accompanying drawings,but it is understood that the present invention should not be limited tothe following embodiments.

[0059]FIG. 3 is a perspective view showing a thin film resonatoraccording to one preferred embodiment of the present invention and FIG.4 is a cross-sectional view showing the thin film resonator in FIG. 3.

[0060] Referring to FIGS. 3 and 4, a thin film resonator 100 accordingto the present invention has a supporting member 190, a first electrode165, a dielectric layer 175 and a second electrode 185. The thin filmresonator 100 is formed on a substrate 110 and a first air gap 200 isinterposed between the thin film resonator 100 and the substrate 110.

[0061] The supporting member 190 supports the thin film resonator 100and includes a supporting layer 155 and a plurality of posts 140 and141. The supporting layer 155 is composed of silicon nitride (AIN) andthe posts 140 and 141 are respectively composed of boro-phosphorsilicate glass (BPSG).

[0062] In the present embodiment, four posts are formed at predeterminedportions of the substrate 110, respectively. The supporting layer 155has the shape of a rectangular plate supported by the posts 140 and 141.

[0063] In addition, a plurality of openings 195 and 196 are formedthrough portions of the supporting layer 155 adjacent to the posts 140and 141 respectively, so that the supporting layer 155 including thoseopenings 195 and 196 performs a stress balancing role to prevent thethin layers of the thin film resonator 100 from bending while severalthin layers are stacked to form the thin film resonator 100. The posts140 and 141 support the supporting layer 155 and the structure thereon,and the first air gap 200 is interposed between the substrate 110 andthe supporting layer 155. As a result, the thin film resonator 100 has athree-dimensional, floating construction, thereby minimizing power lossdue to interference from the substrate 110.

[0064] The first electrode 165, the dielectric layer 175 and the secondelectrode 185 are successively formed on the supporting member 190. Thefirst electrode 165, the dielectric layer 175 and the second electrode185 respectively have rectangular plate shapes.

[0065] The first and the second electrode 165 and 185 are composed ofmetals having good electrical conductivity such as platinum (Pt),tantalum (Ta), platinum-tantalum (Pt—Ta), gold (Au), molybdenum (Mo) ortungsten (W). The dielectric layer 175 is composed of piezoelectricmaterials such as barium titanate (BaTiO₃), zinc oxide (ZnO), aluminumnitride (AIN), lead zirconate titanate (PZT; Pb(Zr, Ti)O₃), leadlanthanum zirconate titanate (PLZT; (Pb, La)(Zr, Ti)O₃). Also, thedielectric layer 175 is composed of electrostrictive materials, forexample lead magnesium niobate (PMN; (Pb(Mg, Nb)O₃). Preferably, thedielectric layer 175 is composed of PZT.

[0066] The first electrode 165 is smaller than the supporting layer 155,and the dielectric layer 175 is smaller than the first electrode 165.Also, the second electrode 185 is smaller than the dielectric layer 175,so that the thin film resonator 100 generally has the shape of apyramid.

[0067] A connecting member 220 is formed from a circuit 205 to thesecond electrode 185 so as to connect the thin film resonator 100 withthe circuit 205 formed on the substrate 110. The connecting member 220has a shape of a bridge to connect the thin film resonator 100 with thesecond electrode 185, so that the thin film resonator 100 has athree-dimensional, floating construction. Both end portions of theconnecting member 220 are bent to contact with the second electrode 185and the circuit 205 respectively. The central portion of the connectingmember 220 has the shape of a reverse ‘U’. That is, the lateral portionsof the connecting member 220 are primarily bent from the central portionof the connecting member 220 in a downward direction, and then thelateral portions of the connecting member 220 are secondarily bent inhorizontal directions, respectively. Hence, the end portions of theconnecting member 220 are attached to the second electrode 185 and thecircuit 205 respectively. The connecting member 220 is composed ofmetals having good electrical conductivity such as platinum, tantalum,platinum-tantalum, gold, molybdenum or tungsten.

[0068] Hereinafter, the method for manufacturing the thin film resonatoraccording to one preferred embodiment of the present invention will bedescribed in detail with reference to the accompanying drawings.

[0069]FIGS. 5A to 5I are cross-sectional views illustrating the methodfor manufacturing the thin film resonator in FIG. 4. In FIGS. 5A to 5I,the various elements have the same reference numerals as in FIGS. 3 and4.

[0070] Referring to FIG. 5A, a first sacrificial layer 120 having thethickness of about 1 to 3 μ, is formed on the substrate 100 by a lowpressure chemical vapor deposition (LPCVD) method. The first sacrificiallayer 120 is composed of poly silicon. In this case, the substrate 110is composed of silicon or an insulating material such as glass orceramic.

[0071] Subsequently, the first sacrificial layer 120 is partially etchedusing a photolithography method or a reactive ion etching method,thereby forming holes 130 and 131 that expose portions of the substrate110. At that time, four holes are formed with reference to FIG. 3 thoughonly two holes 130 and 131 are shown in FIG. 5A.

[0072] Referring to FIG. 5B, a BPSG film 135 is formed on the firstsacrificial layer 120 and in the holes 130 and 131. The BPSG layer 135is formed at temperatures below 500° C. using an LPCVD method. The BPSGlayer 135 has a thickness of approximately 2.0 to 3.0 μm and the holes130 and 131 that expose the substrate 110 are filled with the BPSG layer135.

[0073] Referring to FIG. 5C, the BPSG layer 135 is polished using achemical mechanical polishing method or an etch-back process topartially remove the portion of the BPSG layer 135 formed on the firstsacrificial layer 120. Thus, portions of the BPSG layer 135 only remainsin the holes 130 and 131 formed through the first sacrificial layer 120.The remaining portions of the BPSG layer 135 become the posts 140 and141 for supporting the thin film resonator 100. The posts 140 and 141and the successive supporting layer 155 together form a supportingmember for supporting the thin film resonator 100. In this case, fourposts composed of BPSG are formed as shown in FIG. 3 and the shapes ofthe posts are determined by the shapes of the holes formed through thefirst sacrificial layer 120. Hence, the posts assume the shapes ofsquare pillars when the holes have rectangular cross sections, butassume the posts have the shapes of tubular columns when the holes havecircular cross-sections. Also, when the holes have triangular crosssections, the posts assume the shape of triangular pillars.

[0074] Four posts are formed to enhance the stability of the thin filmresonator 100, however, the number of the posts can be increased orreduced in accordance with the consumer's requirements for structuralstability in the thin film resonator 100 according to another embodimentof the present invention.

[0075] In another embodiment of the present invention, the upper portionof the first sacrificial layer 120 can be partially polished while theBPSG layer 135 is being polished. Therefore, the surface of the firstsacrificial layer 120 becomes more even, thereby enhancing theconsistent flatness of the thin film resonator 100. According to stillanother embodiment of the present invention, the thin film resonator 100can still have an enhanced flatness, even though the upper portion ofthe first sacrificial layer 120 is polished separately after the firstsacrificial layer 120 is coated on the substrate 110.

[0076] Referring to FIG. 5D, a first layer 150 composed of siliconnitride (Si_(x)N_(y)) is formed on the first sacrificial layer 120 andthe posts 140 and 141. The first layer 150 has a thickness ofapproximately 0.1 to 1.0 μm resulting from treatment using a plasmaenhanced chemical vapor deposition (PECVD) method. The first layer 150will be patterned to form the supporting layer 155. According to anotherembodiment of the present invention, the first layer 150 can be composedof low temperature oxide (LTO) such as silicon oxide (SiO_(x)) orphosphor oxide (P₂O₅) at temperatures ranging from approximately 350 to450° C.

[0077] Then, a first metal layer 160 is formed on the first layer 150.The first metal layer 160 is composed of metals having excellentelectrical conductivity and good adhesive strength such as platinum,tantalum, platinum-tantalum, gold, molybdenum or tungsten. The firstmetal layer 160 is formed using a sputtering method or a CVD method tohave a thickness of about 0.1 to 1.0 μm. The first metal layer 160 willbe patterned to form the first electrode 165.

[0078] A second layer 170 is formed on the first metal layer 160. Thesecond layer 170 is composed of dielectric components such aspiezoelectric material or electrostrictive material. The second layer170 is formed by a sol-gel method, a spin coating method, a sputteringmethod or a CVD method to achieve a thickness of about 0.1 to 1.0 μm.The second layer 170 will be patterned to form the dielectric layer 175.The second layer 170 is formed using barium titanate, zinc oxide,aluminum nitride, lead zirconate titanate (PZT), lead lanthanumzirconate titanate (PLZT) or lead magnesium niobate (PMN). Preferably,the second layer 170 is formed by spin coating the PZT, and ismanufactured by a so[-gel method to have a thickness of about 0.4 μm.

[0079] According to another embodiment of the present invention, thesecond layer 170 is heat-treated using a rapid thermal annealing (RTA)method to drive the phase transition of the piezoelectric material orthe electrostrictive material of the second layer 170 after the secondlayer 170 is formed. Hence, the dielectric layer 175 can easily respondto any electric field generated between the first electrode 165 and thesecond electrode 185. Also, the mechanical responsiveness of thedielectric layer 175 can easily transfer energy to the first and thesecond electrodes 165 and 185. That is, the dielectric layer 175converts electrical energy to sound wave energy when an electric fieldis generated between the first electrode 165 and the second electrode185, and voltage is applied to the thin film resonator 100. The soundwave proceeds in the same direction as the electric field, and reflectsfrom the interface between the second electrode 185 and the air, therebyoperating the thin film resonator 100 as a filter.

[0080] Then, a second metal layer 180 is formed on the second layer 170.The second metal layer 180 is composed of a metal identical to the firstmetal layer 160 which could be platinum, tantalum, platinum-tantalum,gold, molybdenum or tungsten. The second metal layer 180 is formed bymeans of a sputtering method or a CVD method so that the second metallayer 180 has a thickness of about 0.1 to 1.0 μm. The second metal layer180 will be patterned to form the second electrode 185.

[0081] Referring to FIG. 5E, after a photo resist (not shown) is coatedon the second metal layer 180 and the photo resist is patterned to forma photo resist pattern, the second metal layer 180 is patterned to havethe shape of a rectangular plate by using the photo resist pattern as anetching mask, thereby forming the second electrode 185 (see FIG. 3).

[0082] Then, the second layer 179 and the first metal layer 160 aresuccessively patterned using the above-described method after the protoresist pattern is removed. Thus, the dielectric layer 175 and the firstelectrode 165 respectively have the shapes of rectangular plates, andare formed as shown in FIG. 3. In this case, the dielectric layer 175 islarger than the second electrode 185 and the first electrode 165 islarger than the dielectric layer 175. Therefore, the first electrode165, the dielectric layer 175 and the second electrode 185 combine toform the shape of a pyramid.

[0083] Referring to FIG. 5F, the first layer 150 is patterned using areactive ion etching method or a photolithography method so as to formthe supporting layer 155 including the openings 195 and 196 that areadjacent to the posts 140 and 141 respectively. At that time, theopenings 195 and 196 are preferably formed during the patterning of thefirst layer 150 that forms the supporting layer 155. However, theopenings 195 and 196 are formed after the supporting layer 155.

[0084] The openings 195 and 196 perform as passages for injecting theetching solution or ions used to etch the first sacrificial layer 120,thereby easily removing the first sacrificial layer 120. This minimizesinterference from the thin film resonator 100 due to the substrate 110,because four openings are formed as shown in FIG. 3.

[0085] Referring to FIG. 5G, the first sacrificial layer 120 is removedby using an etching solution that includes hydrofluoric (HF) acidthrough the openings 195 and 196, and then the thin film resonator 100is formed after a washing and a drying processes are performed. Thefirst sacrificial layer 120 can also be removed by using xenon fluoride(XeF₂) or bromine fluoride (BrF₂). Furthermore, the first sacrificiallayer 120 can be removed by means of an argon laser etching method. Thefirst air gap 200 is formed at the point of the first sacrificial layer120 as the first sacrificial layer 120 is removed. That is, the thinfilm resonator 100 is formed on the substrate 110 and the first air gap200 is interposed between the substrate 110 and the thin film resonator100.

[0086] Referring to FIG. 5H, a second sacrificial layer 210 is coated onthe whole surface of the substrate 110 where the thin film resonator 100is formed as above described after the circuit 205 is created on thesubstrate 110. The second sacrificial layer 210 is composed of polysilicon using an LPCVD method identical to that used to form the firstsacrificial layer 120. In addition, the second sacrificial layer 210 canbe composed of photo resist added using a spin coating method. In thiscase, the surface of the second sacrificial layer 210 can be polished bya chemical mechanical polishing method in order to enhance the flatnessof the second sacrificial layer 210. Also, the surface of the secondsacrificial layer 210 can be planed using an etch-back process.

[0087] Subsequently, the second sacrificial layer 210 is partiallyetched using a photolithography process or an argon laser etchingprocess to partially expose the second electrode 185 of the thin filmresonator 100 and the circuit 205 formed on the substrate 110.

[0088] Referring to FIG. 5I, a third metal layer is formed on theexposed portion of the second electrode 185, the exposed portion of thecircuit 205 and the second sacrificial layer 210. The third metal layeris composed of a metal identical to that of the first metal layer 160such as platinum, tantalum, platinum-tantalum, gold, molybdenum ortungsten. The third metal layer is deposited by a sputtering method or aCVD method so that the third metal layer has a thickness of about 0.1 to1.0 μm.

[0089] Then, the third metal layer is patterned to form the connectingmember 220 that electrically connects the thin film resonator 100 to thecircuit 205 on the substrate 110.

[0090] Subsequently, the second sacrificial layer 210 is removed by anetching solution containing hydrofluoric acid, xenon fluoride, brominefluoride or by suing an argon laser etching method. Then, the thin filmresonator 100, having the connecting member 220 is completed after awashing and a drying process are performed. When the second sacrificiallayer 210 is removed, a second air gap 225 is formed at the point wherethe second sacrificial layer 210 was positioned, so that the second airgap 225 is interposed between the substrate 110, the thin film resonator100 and the connecting member 220.

[0091] In one preferred embodiment of the present invention, after thefirst sacrificial layer 120 is removed, the connecting member 220 isformed on the second sacrificial layer 210, and then the secondsacrificial layer 210 is removed. However, according to anotherembodiment of the present invention, the first and the secondsacrificial layers 120 and 210 are simultaneously removed after theconnecting member 220 is formed on the second sacrificial layer 210without removing the first sacrificial layer 120. By using thisproduction method, the manufacturing time and costs can be reduced.

[0092] While this invention has been described and shown as havingmultiple designs, the present invention may be further modified withinthe spirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains.

[0093] Industrial Applicability

[0094] As it is described above, the thin film resonator of the presentinvention is manufactured using the MEMS technology without etching thesubstrate to have minute dimensions under hundreds of micro meters.Hence, the thin film resonator is exceptionally small and can be highlyintegrated onto the substrate.

[0095] Also, the thickness of the dielectric layer of the thin filmresonator can be adjusted to achieve the integration of the multiplebands including radio frequency (RF), intermediate frequency (IF) andlow frequency (LF) by controlling the thickness of the dielectric layer.Also, an inductor and a capacitor can be integrated.

[0096] In addition, the yield can be increased and the manufacturingcosts greatly reduced since the thin film resonator can be manufacturedwithout etching or machining the silicon substrate. Therefore, themanufacturing process of the present invention has excellent advantagesduring mass production, including simplicity and ease of packaging.

[0097] Also, the thin film resonator of the present invention has a goodquality factor of about 1000 to 10000 and a low insertion loss of under2 dB because the thin film resonator has minute patterns and athree-dimensional, floating construction that is easily manufactured bythe MEMS technology.

[0098] Furthermore, the thin film resonator of the present invention canminimize interference from the substrate and has ideal dimensionsbecause of its compact substrate, making the thin film resonatorexceptionally small. Yet having a three-dimensional, floatingconstruction.

1. A thin film resonator for filtering frequencies of a predeterminedband, which comprises: a supporting means having a plurality of postsformed on a substrate and a supporting layer formed on said posts; afirst electrode formed on said supporting means; a dielectric layerformed on said first electrode; and a second electrode formed on saiddielectric layer.
 2. The thin film resonator as recited in claim 1,wherein four posts are formed on said substrate so that said supportinglayer is supported by said four posts and a plurality of openings areformed through said supporting layer.
 3. The thin film resonator asrecited in claim 1, wherein said posts are respectively composed ofboro-phospher silicate glass and said supporting layer is composed ofsilicon nitride.
 4. The thin film resonator as recited in claim 1,wherein said supporting layer, said first electrode, said dielectriclayer and said second electrode are shaped like rectangular plates. 5.The thin film resonator as recited in claim 4, wherein said firstelectrode is smaller than said supporting layer, said dielectric layeris smaller than said first electrode, and said second electrode issmaller than said dielectric layer.
 6. The thin film resonator asrecited in claim 4, wherein said supporting layer, said first electrode,said dielectric layer and said second electrode combine to form apyramid shape.
 7. The thin film resonator as recited in claim 1, whereinsaid first electrode is composed of metals selected from the groupconsisting of platinum, tantalum, platinum-tantalum, gold, molybdenumand tungsten.
 8. The thin film resonator as recited in claim 1, whereinsaid second electrode is composed of metals selected from the groupconsisting of platinum, tantalum, platinum-tantalum, gold, molybdenumand tungsten.
 9. The thin film resonator as recited in claim 1, whereinsaid first and said second electrodes are composed of the same metalshaving electrical conductivity and adhesion strength.
 10. The thin filmresonator as recited in claim 1, wherein said dielectric layer iscomposed of materials selected from the group consisting of bariumtitanate (BaTiO₃), zinc oxide (ZnO), aluminum nitride (AIN), leadzirconate titanate (Pb(Zr, Ti)O₃), lead lanthanum zirconate titanate((Pb, La)(Zr, Ti)O₃) and lead magnesium niobate (Pb(Mg, Nb)O₃).
 11. Thethin film resonator as recited in claim 1, further comprising aconnecting means for connecting said second electrode to a circuitformed on said substrate.
 12. The thin film resonator as recited inclaim 11, wherein a first air gap is interposed between said substrateand said supporting means and a second air gap is interposed betweensaid second electrode and said connecting means.
 13. The thin filmresonator as recited in claim 11, wherein said connecting means having acentral portion and lateral potions bent from the central portion sothat said connecting means contacts with said circuit and said secondelectrode.
 14. The thin film resonator as recited in claim 11, whereinsaid connecting means is composed of metals selected from the groupconsisting of platinum, tantalum, platinum-tantalum, gold, molybdenumand tungsten.
 15. A method for manufacturing a thin film resonator forfiltering frequencies of a predetermined band, which comprises the stepsof: forming a first sacrificial layer on a substrate; partially etchingsaid first sacrificial layer to expose portions of said substrate;forming a plurality of posts on the exposed portions of said substrate;forming a first layer on said posts and said first sacrificial layer;forming a first metal layer on said first layer; forming a second layeron said first metal layer; forming a second metal layer on said secondlayer; forming a first electrode, a dielectric layer and a secondelectrode by patterning said second metal layer, said second layer andsaid first metal layer; forming a supporting layer having a plurality ofopenings by patterning said first layer; and removing said firstsacrificial layer through said openings.
 16. The method formanufacturing a thin film resonator as recited in claim 15, wherein saidfirst sacrificial layer is composed of poly silicon and formed by a lowpressure chemical vapor deposition method.
 17. The method formanufacturing a thin film resonator as recited in claim 15, wherein saidfirst sacrificial layer is partially etched by a photolithographymethod, a reactive ion etching method or an argon laser etching method.18. The method for manufacturing a thin film resonator as recited inclaim 15, wherein the step for forming said posts further comprises:forming a BPSG layer on said first sacrificial layer and said substrate;and polishing said BPSG layer to remove portions of said BPSG layerformed on said first sacrificial layer.
 19. The method for manufacturinga thin film resonator as recited in claim 18, wherein said BPSG layer isformed by a low pressure chemical vapor deposition layer at temperaturesunder approximately 500° C.
 20. The method for manufacturing a thin filmresonator as recited in claim 18, wherein said BPSG layer is polished bya chemical mechanical polishing method or etch-back method.
 21. Themethod for manufacturing a thin film resonator as recited in claim 15,wherein said first layer is formed by a plasma enhanced chemical vapordeposition method.
 22. The method for manufacturing a thin filmresonator as recited in claim 15, wherein said first layer is formed byusing silicon oxide or phosphor oxide at temperatures of about 350 toabout 450° C.
 23. The method for manufacturing a thin film resonator asrecited in claim 15, wherein said first and said second electrodes areformed from metals selected from the group consisting of platinum,tantalum, platinum-tantalum, gold, molybdenum and tungsten and by usinga sputtering method or a chemical vapor deposition method.
 24. Themethod for manufacturing a thin film resonator as recited in claim 15,wherein said second layer is formed from piezoelectric material orelectrostrictive material and by using a sol-gel method, a spin coatingmethod, sputtering method or a chemical vapor deposition method.
 25. Themethod for manufacturing a thin film resonator as recited in claim 24,wherein said second layer is composed of material selected from thegroup consisting of barium titanate, zinc oxide, aluminum nitride, leadzirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT) andlead magnesium niobate (PMN).
 26. The method for manufacturing a thinfilm resonator as recited in claim 15, wherein the step for forming saidsecond layer further comprises heat treating said second layer by usinga rapid thermal annealing method for phase transition of said secondlayer.
 27. The method for manufacturing a thin film resonator as recitedin claim 15, wherein said first sacrificial layer is removed using xenonfluoride or bromine fluoride.
 28. The method for manufacturing a thinfilm resonator as recited in claim 15, further comprising the steps of:forming a second sacrificial layer on said substrate and said secondelectrode; partially etching said second sacrificial layer to expose aportion of said second electrode and a circuit formed on said substrate;forming a connecting means for connecting said second electrode to saidcircuit; and removing said second sacrificial layer.
 29. The method formanufacturing a thin film resonator as recited in claim 28, wherein saidsecond sacrificial layer is composed of poly silicon or photo resist andformed by using a low pressure chemical vapor deposition method or aspin coating method.
 30. The method for manufacturing a thin filmresonator as recited in claim 28, further comprising the step ofplanarizing the surface of said second sacrificial layer by using achemical mechanical polishing method or an etch-back method.
 31. Themethod for manufacturing a thin film resonator as recited in claim 28,wherein said connecting means is formed by using metals selected fromthe group consisting of platinum, tantalum, platinum-tantalum, gold,molybdenum and tungsten and by using a sputtering method or a chemicalvapor deposition method.
 32. The method for manufacturing a thin filmresonator as recited in claim 28, wherein said second sacrificial layeris removed by using xenon fluoride, bromine fluoride, or an etchingsolution including hydrofluoric acid or by using an argon laser etchingmethod.
 33. The method for manufacturing a thin film resonator asrecited in claim 28, wherein the steps for removing said first and saidsecond sacrificial layers are simultaneously performed.